Reroofing over Asphalt Shingles

The key to a flat roof is a filler strip in the first course

Starting Out Right
The efficiency of the job and the longevity of the roof
depend on carefully laying down the starter courses along the
eaves. To prevent ice dams up here in snow country, we first
run out a 36-inch-wide layer of AC EavesSeal (NEI, 50 Pine Rd.,
Brentwood, NH 03833; 800/998-4634; www.nei-act.com). Intended
for reroof work, this membrane has a 4-inch-wide self-adhesive
leading edge that adheres to the new drip edge; the top edge is
nailed (Figure 3).
Figure
3. To guard against damage from ice dams, a 36-inch-wide
strip of bituminous membrane is rolled out along the eaves.
After lightly nailing the top edge, the membrane’s
4-inch-wide adhesive strip is pressed onto the new drip edge to
form a tight seal.

Efficient layout.

While
the membrane is being applied, my crew chief will "map out" the
roof to find the most efficient and most attractive layout for
the shingles. Many roofers simply start at the rake edge with a
full shingle and let the tabs fall where they may. I do the
same with architectural shingles, because there are no tabs to
align. But with tabbed shingles, I prefer to shingle outward
from a pair of vertical center lines. This not only enables me
to keep two people nailing without tripping over each other, it
assures me that the shingle tabs will align vertically because
they won’t be affected by any waviness in the rake edge.
It also means the shingles on the ends of each course will be
close to the same width. We do, however, measure back to the
rake edges and to any dormers, skylights, or chimneys to make
sure we won’t end up with skinny tabs, which invariably
break off and look terrible. After making any adjustments back
and forth, we snap the center line, then a second, parallel
line 6 inches over — it doesn’t matter which side.
To create a stepped pattern, succeeding courses will alternate
between these lines as we work our way up the roof.

Butting up.

For the new
roof to lay flat, the top edges of the new shingles must butt
up against the tabs of the old ones . The trick is to use
precut "invert" shingles as filler strips. Beginning at one
vertical chalk line, we use 5-inch-wide "inverts," tar spots
pointed towards the eaves, and align the bottom edge with the
drip edge. This course gets nailed at the bottom, just above
the tar spots.
The first full course is aligned with the second chalk line.
Because earlier we cut the top layer of existing shingles back
12 inches from the eaves, we can run full-width shingles,
overlaying the inverts and laid flush with the drip edge. The
second full-width course of shingles is laid out back at the
first chalk line and butted up against the bottom edge of the
fourth course of old shingles. We butt up succeeding courses
until we get above the 36-inch-wide eaves membrane, at which
point we can really fly.

Pyramid pattern.

Despite the manufacturers’ assurances, we find that
shingle sizes are inconsistent. To ensure straight vertical
lines, and to avoid that wavy pattern you see when material
varies from bundle to bundle, we lay our shingle courses in a
pyramid shape . We start by running one column of three-tab
shingles nearly all the way up to the ridge, alternating each
course back and forth between the two chalk lines. Returning to
the bottom, we cover a triangular area on each side of the
column, stacking six courses of three-tab, two-tab, and one-tab
shingles. Next, we fill in with full shingles until our courses
reach the top of the pyramid, then we repeat the procedure.

Reroof nailing.

On an
average job, we run three air nailers off one Emglo gas-powered
compressor (Emglo Air Compressors, 303 Industrial Park Rd.,
Johnstown, PA 15904; 814/269-1000) that we leave on the ground.
To keep the hoses from tangling, we run one thick lead hose
from the compressor to the roof and branch off from there.
We use standard round head roofing nails in our guns, 11/2
inches long when we’re covering one layer of old roofing,
13/4 inches for two layers. Condensation forms on the tips of
nails that protrude into attics, so I try to use the shortest
nails possible. We follow standard nailing patterns —
four nails per shingle with the two center nails located just
above the cutouts. The exception is at the edges, where we hold
our nails back 11/2 inches instead of the 1 inch called for by
roofing manufacturers.
Shingles are nailed with pneumatic coil nailers. Because
the existing roof has some give to it, nails are held back 11/2
inches from the shingle edges to avoid creating dips that can
be seen from the ground.
We do this because we are nailing over a resilient surface,
and when the nails are placed too close together they can make
a depression that can be seen from the ground. There is no
disadvantage to spreading the nails out as little as we do.
Valleys. Before our shinglers
reach a valley, we flash it with a 36-inch-wide layer of
90-pound mineral-surfaced roll roofing. If it’s a
full-length valley, we lap the flashing over the eaves membrane
and run it to the drip edge. If it’s a dormer, we run the
flashing past the beginning of the valley and lap it over the
new shingles in the course below.
When it comes to shingling a valley, I prefer the closed-cut
approach because it offers the best combination of protection
and efficiency. To make a closed-cut valley, we run up all the
shingles for one side, making sure they extend at least one
full tab (12 inches) past the centerline of the valley (Figure
6).
Figure
6. Valleys are first flashed with 90-pound roll roofing.
Then shingles from one roof plane are laid so they extend one
tab beyond the valley center. Shingles from the other roof
plane are overlaid, then cut back with a hooked knife to form a
"closed" valley.
We also make sure to keep all of our nails at least 8 inches
back from the center. When we do the other side, we run all the
shingles far enough so that we can snap a chalk line through
the center of the valley and cut a nice straight line with a
hooked roofing blade. When we do a dormer, we always run up the
dormer shingles first so the water from the main roof
can’t run under the dormer shingles.

Permanent flashing.

When I was young and foolish, I used to take pride that I cared
enough to cut loose all the old step flashing and reweave it
into the new roofing. It cost a lot of money to do that, and
the homeowners never noticed it, so I stopped. The truth is, as
long as the flashing was done right the first time and
hasn’t rotted away, it’s better left in place.
When we shingle up to dormers, chimneys, or skylights, we
still peel up the bottom edge of the flashing and tuck the new
roofing underneath. Then, as we work our way up the sides, we
bed each shingle down onto a thick bead of roof cement along
the edge where the shingle meets the wall line. We also lay a
large bead of tar under the shingles where they meet the head
flashing. Contrary to popular belief, as long as the cement is
covered by the roofing, it will serve for the life of the
roof.

Capping Off

When we reach
the top of the roof, we fold the last courses over the ridge
and cover them with cap shingles. To ensure a straight line, we
measure down 6 inches from the center of the ridge on the most
visible side, and snap a line. We run cap shingles from one end
of the roof to the other, aligning the edges with the chalk
line, and placing one nail on either side of the ridge, just
behind the tar strip, which will be covered by the next
shingle. The final cap will be a 5-inch piece or less, and we
cover the exposed nails with tar.

Ventilation.

When the
attic needs more ventilation, I like to install a low-profile
shingle-over ridge vent, because it does the job, yet blends
into the roofline. We like either the Omni-Ridge (Lomanco, P.O.
Box 519, Jacksonville, AR 72076; 800/643-5596; www.lomanco.com)
or the ShingleVent II (Air Vent, 4801 N. Prospect Rd., Peoria
Heights, IL 61614; 800/247-8368), because they both have an
external baffle that keeps snow and driven rain out of the
attic. After the roofing and sheathing are cut out, we hold the
ridge vent to the same chalk line as the caps and nail it in
place. We run cap shingles over the top of the vent, using
21/2-inch roofing nails to reach the sheathing.

Customer Satisfaction

No
job is successful unless the customer is satisfied. At the end
of every day, we sweep up the site and pick up nails from the
driveway and short grass with a Magnet Nail Sweeper (Hilco,
P.O. Box 1789, Hickory, NC 28603; 704/328-8141). When the job
is finished, we do a final sweep from the ridge down with a
wide soft-bristle broom. We also clear roof debris from the
gutters and thoroughly sweep the driveway, front steps,
walkways, and anywhere else debris may have settled. We want it
to look like we were never there, so we make sure to put
anything that we had to move back in its place.
Finally, before the last ladder is taken down, I take a can
of black or aluminum and paint the vent pipes, chimney
flashing, and furnace flange. This not only makes my work look
its best on the day I leave the job, but it prevents rust
stains from making my work look bad in the future.
John Curran and his wife, Jan, own and operate RSI
General Contractors, a Syracuse, N.Y., roofing, siding, and
insulation company founded in 1978.